Python 操作 PostgreSQL 数据库

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我使用的是 Python 3.7.0

 

PostgreSQL可以使用psycopg2模块与Python集成。

sycopg2是用于Python编程语言的PostgreSQL数据库适配器。 

psycopg2是非常小,快速,稳定的。 您不需要单独安装此模块,因为默认情况下它会随着Python 2.5.x版本一起发布。

pip3 install python-psycopg2
pip3 install psycopg2-binary

 

连接到数据库

以下Python代码显示了如何连接到现有的数据库。 如果数据库不存在,那么它将自动创建,最后将返回一个数据库对象。

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")

print("Opened database successfully")

在这里指定使用testdb作为数据库名称,如果数据库已成功打开连接,则会提供以下消息:

Open database successfully

创建表

以下Python程序将用于在先前创建的数据库(testdb)中创建一个表:

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print("Opened database successfully")

cur = conn.cursor()
cur.execute(‘‘‘CREATE TABLE COMPANY
       (ID INT PRIMARY KEY     NOT NULL,
       NAME           TEXT    NOT NULL,
       AGE            INT     NOT NULL,
       ADDRESS        CHAR(50),
       SALARY         REAL);‘‘‘)
print "Table created successfully"

conn.commit()
conn.close()

 

当执行上述程序时,它将在数据库testdb中创建COMPANY表,并显示以下消息:

Opened database successfully
Table created successfully
 

插入操作

以下Python程序显示了如何在上述示例中创建的COMPANY表中创建记录:

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print("Opened database successfully")

cur = conn.cursor()

cur.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) 
      VALUES (1, Paul, 32, California, 20000.00 )");

cur.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) 
      VALUES (2, Allen, 25, Texas, 15000.00 )");

cur.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) 
      VALUES (3, Teddy, 23, Norway, 20000.00 )");

cur.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) 
      VALUES (4, Mark, 25, Rich-Mond , 65000.00 )");

conn.commit()
print("Records created successfully");
conn.close()

 

当执行上述程序时,它将在COMPANY表中创建/插入给定的记录,并显示以下两行:

Opened database successfully
Records created successfully
 

SELECT操作

以下 Python 程序显示了如何从上述示例中创建的 COMPANY 表中获取和显示记录:

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print("Opened database successfully")

cur = conn.cursor()

cur.execute("SELECT id, name, address, salary  from COMPANY")
rows = cur.fetchall()
for row in rows:
   print("ID = ", row[0])
   print("NAME = ", row[1])
   print("ADDRESS = ", row[2])
   print("SALARY = ", row[3], "
")

print("Operation done successfully");
conn.close()

 

执行上述程序时,会产生以下结果:

Opened database successfully
ID =  1
NAME =  Paul
ADDRESS =  California
SALARY =  20000.0

ID =  2
NAME =  Allen
ADDRESS =  Texas
SALARY =  15000.0

ID =  3
NAME =  Teddy
ADDRESS =  Norway
SALARY =  20000.0

ID =  4
NAME =  Mark
ADDRESS =  Rich-Mond
SALARY =  65000.0

Operation done successfully

 

 

更新操作

以下 Python 代码显示了如何使用UPDATE语句来更新任何记录,然后从COMPANY表中获取并显示更新的记录:

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print("Opened database successfully")

cur = conn.cursor()

cur.execute("UPDATE COMPANY set SALARY = 25000.00 where ID=1")
conn.commit
print("Total number of rows updated :", cur.rowcount)

cur.execute("SELECT id, name, address, salary  from COMPANY")
rows = cur.fetchall()
for row in rows:
   print("ID = ", row[0])
   print("NAME = ", row[1])
   print("ADDRESS = ", row[2])
   print("SALARY = ", row[3], "
")

print("Operation done successfully");
conn.close()

 

Python

执行上述程序时,会产生以下结果:

Opened database successfully
Total number of rows updated : 1
ID =  1
NAME =  Paul
ADDRESS =  California
SALARY =  25000.0

ID =  2
NAME =  Allen
ADDRESS =  Texas
SALARY =  15000.0

ID =  3
NAME =  Teddy
ADDRESS =  Norway
SALARY =  20000.0

ID =  4
NAME =  Mark
ADDRESS =  Rich-Mond
SALARY =  65000.0

Operation done successfully
 

删除操作

以下 Python 代码显示了如何使用 DELETE 语句来删除记录,然后从 COMPANY 表中获取并显示剩余的记录:

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print("Opened database successfully")

cur = conn.cursor()

cur.execute("DELETE from COMPANY where ID=2;")
conn.commit
print("Total number of rows deleted :", cur.rowcount)

cur.execute("SELECT id, name, address, salary  from COMPANY")
rows = cur.fetchall()
for row in rows:
   print("ID = ", row[0])
   print("NAME = ", row[1])
   print("ADDRESS = ", row[2])
   print("SALARY = ", row[3], "
")

print("Operation done successfully");
conn.close()

 

执行上述程序时,会产生以下结果:

Opened database successfully
Total number of rows deleted : 1
ID =  1
NAME =  Paul
ADDRESS =  California
SALARY =  20000.0

ID =  3
NAME =  Teddy
ADDRESS =  Norway
SALARY =  20000.0

ID =  4
NAME =  Mark
ADDRESS =  Rich-Mond
SALARY =  65000.0

Operation done successfully

https://www.yiibai.com/postgresql/postgresql_python.html




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